Mitsurugi: if we're talking about short term peak, I'm not sure Lasker ever had a limited span of dominance to match Fischer in the early 1970's, Capablanca circa 1918-1924 or Morphy's brilliant, albeit transient, reign. I always thought his real achievement was holding the world championship for 27 years, and remaining one of the world's very best for even longer.
As for quality of play, I don't think anyone would rate Lasker, Capablanca or Alekhine as lacking in quality (a few might do so for Morphy or Steinitz but concensus seems to hold steady for them as well). Even though chess theory might have advanced, especially in terms of opening theory, one merely has to look through their games: their strength speaks for itself.
Also, if you wanted to, you could go with computer analysis, which, I believe, shows that Capablanca had the lowest error rate among all the world champions...
RJF.